efivarfs: Rate limit statfs() handler

Ravi reports that statfs() may be called by unprivileged users on the
efivarfs mount point, which may result in a flood of calls to the
QueryVariableInfo() runtime service. These calls are disproportionately
costly on x86 systems where the variable store is backed by SMM, as each
SMM entry requires a rendez-vous of all the CPUs.

So rate limit the calls to QueryVariableInfo() at twice per second, and
return the most recently obtained value for calls that are elided.

Cc: <stable@vger.kernel.org>
Reported-by: Ravi Bangoria <ravi.bangoria@amd.com>
Fixes: d86ff3333cb1 ("efivarfs: expose used and total size")
Reviewed-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

0 files changed, 0 insertions, 0 deletions